This invention relates to systems used to detect and locate failures of the cladding of fuel rods in nuclear fuel assemblies used in nuclear reactors, especially sodium cooled nuclear reactors.
Nuclear reactors contain a fuel core which is a grouping of fuel assemblies each of which has a plurality of fuel rods. A fuel rod is a cylindrical, metal tube which contains nuclear fuel pellets. The metal of the tube separates the fuel pellets from reactor coolant which flows over the surface of the tube or cladding.
A penetration of the cladding, termed a fuel failure, may allow fission fragments, particularly gases, to escape from the fuel rod into the reactor coolant. These gases may mingle with the gas contained in a cover gas region which is usually a feature of liquid metal cooled reactors.
Nuclear reactors are expected to experience fuel failure in spite of rigorous quality control and conservative operating procedures. Most of the failures result from pin-hole cracks in the cladding and/or end plug welds. Such failures are now detected by analysis of fission-gas outside the core (e.g., in the reactor cover gas) and by observation of delayed neutron precursors in the reactor coolant.
One of the problems faced by reactor instrumentation is to detect and monitor failed fuel in such a manner that safe operation of the reactor is not impaired. This problem can be solved by having the ability to quickly obtain and analyze samples of fission gas released by failed fuel. There is a major need to locate the leaking fuel assembly rapidly in order to expedite its removal and minimize reactor down time.
Consequently, it is desired to provide a method for obtaining a sample of fission gas from reactor coolant and quickly identify the leaking assembly.